| [Purpose]: To investigate the optimal alignment methods and planning target volume (PTV) margins for the treatment of rectal cancer, observe the motions of normal tissues and organs, and analyze their impact on treatment by using image-guided radiotherapy (IGRT).[Materials and Methods]: Ten patients with rectal cancer were treated with IGRT, and 82 imagings were obtained from this study. The difference in bone alignment, grey value alignment and manual alignment was compared. The study also analyzed the setup errors and PTV margins. The sacrococcyx, bladder and rectum were contoured on all CT scans to examine their volume and position changes, and to evaluate their impact on the treatment.[Results]: There was no statistical difference between the three alignment methods. The comparisons of setup errors before or after correction were 2.2±3.2/-0.2±1.5mm in the vertical direction, 2.4±3.4/1.0±2.3mm in lateral direction and 3.9±4.9/0.6±3.0mm in longitudinal direction. The setup margins were 8.5/5.2mm, 9.5/7.7mm and 14.6/11.2mm, respectively. The average bladder volumes after the CT simulation and CBCT were 544.84±197.16 cm~3 and 440.79±207.89 cm~3, respectively. The difference between the treatments can reach as high as 4.4 times for the same patient. The bladder volume was related to the ratio of the bladder to CTV and V50. However, there was no significant relationship with the ratio of sacrococcyx and rectum to CTV. The average volumes of rectum for simulation CT and CBCT were 161.77±60.79cm~3 and 133.44±50.78cm~3, respectively. The difference between the treatments can reach as high as 1.8 times for the same patient.[Conclusions]: There was no statistical difference between the three alignment methods for rectal cancer target. Due to less time consuming, the bone alignment should be used in the treatment. PTV margins can be reduced by using IGRT. Volumes of the bladder and rectum were observed to have a relatively significant variation during the treatment. |
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